implement postOrder

Author: happy-san

Diff for: lib/trees/threaded_binary_tree.dart

@@ -159,6 +159,20 @@ class ThreadedBinaryTree<V extends Comparable>
     return result;
   }
 
+  @override
+  List<V> postOrder() {
+    var result = <V>[];
+    _postOrder(root, result);
+    return result;
+  }
+
+  void _postOrder(ThreadedBinaryNode<V>? node, List<V> list) {
+    if (node == null) return;
+    if (!(node.leftIsThread ?? false)) _postOrder(node.left, list);
+    if (!(node.rightIsThread ?? false)) _postOrder(node.right, list);
+    list.add(node.value!);
+  }
+
   @override
   List<V> preOrder() {
     var result = <V>[];

Diff for: test/trees/threaded_binary_tree_test.dart

@@ -31,8 +31,8 @@ void main() {
   });
 
   test('Test single node', () {
-    expect(singleNode.root!.value, equals(0));
-    expect(multipleNodes.root!.value, equals('l'));
+    expect(singleNode.root!.value, equals('@'));
+    expect(multipleNodes.root!.value, equals('f'));
   });
 
   test('Nullify', () {
@@ -43,8 +43,8 @@ void main() {
 
   test('Check contains', () {
     expect(empty.contains(''), isFalse);
-    expect(singleNode.contains('@'), isFalse);
-    expect(singleNode.contains(''), isTrue);
+    expect(singleNode.contains('@'), isTrue);
+    expect(singleNode.contains(''), isFalse);
     expect(multipleNodes.contains('nope'), isFalse);
 
     for (var i in ['f', 'b', 'g', 'a', 'd', 'i', 'c', 'e', 'h']) {
@@ -60,13 +60,12 @@ void main() {
           equals(<String>['f', 'b', 'a', 'd', 'c', 'e', 'g', 'i', 'h']));
     });
 
-    // Results in stack overflow.
     test('Post-order', () {
       expect(empty.postOrder(), <String>[]);
       expect(singleNode.postOrder(), <String>['@']);
       expect(multipleNodes.postOrder(),
           equals(<String>['a', 'c', 'e', 'd', 'b', 'h', 'i', 'g', 'f']));
-    }, skip: true);
+    });
 
     test('In-order', () {
       expect(empty.inOrder(), <String>[]);
@@ -169,6 +168,32 @@ void main() {
     var list = multipleNodes.inOrder();
 
     multipleNodes.delete('f');
-    expect(multipleNodes.inOrder(), (list..remove('m')));
+    expect(multipleNodes.inOrder(), equals(list..remove('f')));
+
+    multipleNodes.delete('a');
+    expect(multipleNodes.inOrder(), equals(list..remove('a')));
+
+    multipleNodes.delete('i');
+    expect(multipleNodes.inOrder(), equals(list..remove('i')));
+
+    multipleNodes.delete('c');
+    expect(multipleNodes.inOrder(), equals(list..remove('c')));
+
+    multipleNodes.delete('e');
+    expect(multipleNodes.inOrder(), equals(list..remove('e')));
+
+    multipleNodes.delete('d');
+    expect(multipleNodes.inOrder(), equals(list..remove('d')));
+
+    multipleNodes.delete('b');
+    expect(multipleNodes.inOrder(), equals(list..remove('b')));
+
+    multipleNodes.delete('g');
+    expect(multipleNodes.inOrder(), equals(list..remove('g')));
+
+    multipleNodes.delete('h');
+    expect(multipleNodes.inOrder(), (list..remove('h')));
+
+    expect(multipleNodes.isEmpty, isTrue);
   });
 }